Various localization technologies have been developed or suggested for tracking mobile devices in indoor environments. However, conventional localization technologies often fall short in user experience, cost, or security. For example, although global positioning systems (GPS) may provide an acceptable user experience in outdoor environments, it is energy consuming and may suffer from frequent satellite disconnections indoors. Wi-Fi triangulation techniques have been unable to achieve accurate results with sub-second update times and thus may be unreliable for mobile devices frequently in motion. Radio-frequency identification (RFID) suffers from a relatively short communication range, a lack of extensibility, and may be world-readable introducing security concerns. Even device-centric localization techniques, for example, dead reckoning, may be prone to failure due to calibration issues and unwanted interference.
Localization techniques have also been proposed based on received signal strength indicators (RSSI). RSSI is a measurement of the strength of a received signal at the mobile device from a node such as an access point or Bluetooth low energy (BLE) beacon. In some instances, the determined power of the signal may be used to calculate a coarse-grained distance from the node. However, recent research has shown that conventional RSSI technology gives unacceptably high errors, and thus is unreliable for indoor sensor localization.